In this photo provided by the European Space Agency, ESA, Monday Jan. 20, 2014 technicians celebrate after receiving the Rosetta wake up signal in the control room of ESA in Darmstadt, Germany. Waking up after almost three years of hibernation, a comet-chasing spacecraft sent its first signal back to Earth on Monday, prompting cheers from scientists who hope to use it to achieve the first landing on a comet.The European Space Agency received the all-clear message from its Rosetta spacecraft at 7:18 p.m. (1818 GMT; 1:18 p.m. EST) _ a message that had to travel some 800 million kilometers (500 million miles). (AP Photo/ESA, Juergen Mai, File)

Scientists at the European Space Agency are expecting their comet-chasing probe Rosetta to wake from almost three years of hibernation at 11 a.m. Monday Jan. 20, 2014 (1000 GMT; 5 a.m. EST) and phone home to say all is well. The scientists are facing an agonizing wait of several hours until the first signal reaches Earth. (AP Photo/dpa, Daniel Reinhardt)